White balance involves the process of removing unrealistic color casts from images so that objects which appear white in person are rendered white in the image. Improper white balance can create unsightly blue, orange, or even green color casts. Proper white balance takes into account the color temperature of a light source, which refers to the relative warmth or coolness of the light—light sources, also referred to as illuminants herein, may not be pure white, but instead have a bias towards a particular color. Human perception is able to compensate for illumination that is not pure white, so colors appear relatively consistent over a wide range of lighting conditions.
Cameras, however, may perceive the same scene differently when the illuminant changes. A typical sensor used in an electronic image capture device, such as a digital camera or video recorder, may capture an image that exhibits a color shift attributable to illumination from a non-pure white source. The color shift exhibited in the captured image may appear unnatural to the human eye and create a perception that the sensor or capture device is of low quality due to being unable to accurately capture real world images.
Cameras perform automatic white balance (AWB) to attempt to determine what objects are white when illuminated by light sources of different color temperatures. A captured image may be processed to compensate for lighting conditions and color temperature of the illuminant. White balance compensation depends on the color temperature of the illuminant. White balance compensation configured for an illuminant at a first color temperature may not correct for color temperature of a second illuminant, and may further degrade image quality by introducing additional color shift into the image. When color tone in a digital image is off, for example due to no white balancing or incorrect white balancing, human perception of the image may be objectionable.